Extreme Drought of 2018 in Central Europe: Evaluation and Predictability

Recent years in Central Europe have been strongly affected by several prolonged episodes of drought (e.g. 2010; 2012; 2015; 2017 and 2018). There are a few common aspects of weather conditions that play important role in the repeated occurrence of drought conditions in the region: 1) warm winters with decreased extent, thickness and presence of snow; 2) rapid onset of the spring season with above average temperatures and a lack of rain; 3) hot and dry summers with heatwaves and extended periods with little or no precipitation. The summer heatwave of 2015 strongly impacted different sectors of economy and demonstrated growing need for tools that enable continuous monitoring of drought with all its complexity and also provides drought forecast. The year 2018 has again brought the weather with temperatures above and precipitation below their long-term means in large parts of Central Europe. We investigate the impact of these weather conditions on the drought evolution in the Czech Republic during the year 2018.

The winter season 2017/2018 was dry, poor on snow and warmer than long-term mean of 1981-2010. The deficit of precipitation has been growing since January and the cumulative sum of precipitation reached only 50-75% of its long-term mean till the end of August. In addition, most of rain since April came in a form of short (but strong) rain showers or thunderstorms that couldn’t reduce did not bring enough precipitation to alleviate growing drought water deficit in the soil. Long lasting large scale precipitation events, e.g., associated with passing atmospheric fronts, was were practically missing. The year 2018 has been warmer than normal so far. More than 80% of days have been warmer than the long-term normal within the growing season in 2018. The combination of the precipitation deficit and unusually long period with temperatures strongly above the long-term normal has been further amplifying drought conditions.

The combination of warmer and drier weather in the first half of 2018 quickly led to the soil moisture deficit that was significant already during the spring season. Extreme drought conditions remained till the end of August, i.e., almost for the rest of the growing season, and affected the crop yields. The drought evolution within the year is presented by products of operational drought monitoring system called InterSsucho (www.intersucho.cz) where not only soil water content but also condition of vegetation and impacts on crops and yields of major commodities can be studied in daily/weekly steps. We also investigate the forecast component of the InterSucho system that consists of five numerical weather prediction models offering an outlook up to 9 days ahead. The InterSsucho forecast has been important tool for farmers in mitigating negative impacts of drought in 2018. Thus we also discuss a forecast score of the model ensemble to capture the drought development.